Method of drilling wells



Feb. 15, 1944. H. 1.. REED METHOD OF DRILLING WELLS Filed July 25, 1936 2 Sheets-Sheet 1 a Ham/m0 L. REED.

swam/kw F l 5.5. 3% f M 1 ma t gmm uvwam L. J

Feb. 15, 1944.

Patented Feb. 15, 1944 UNITED STATES PATENT OFFICE METHOD OF DRILLING WELLS Howard L. Reed, Houston, Tex., assignor of eleven and one-third per cent to Fohs Oil Company,

Houston, Tex.

Application July 25, 1936, Serial No. 92,541

Claims.

This invention relates to a method of drilling and producing wells, and relates particularly to washing a well and to controlling the same by controlling the characteristics of the washing fluid.

Ordinarily in drilling a well a mud is circulated down through the drill stem and up through the casing to wash out cuttings, etc., and the weight of this mud is controlled by adding heavy material to increase its hydraulic pressure upon the well formations when it is suspected that high formation pressures may be encountered.

Use of this mud puts a great burden on the pump used for circulating it, and it is very difficult to keep in proper condition. If too great a pressure is allowed to be placed upon the formation, the mud will enter and sometimes permanently choke the formation, but if too low a pressure is maintained the well will blow out. It is necessary therefore to maintain exactly the proper mud pressure on the formation, a very difficult and sometimes impossible thing to do.

It is an object of this invention to eliminate the use of a heavy circulating medium, such as one containing suspended weight material, for controlling formation pressures and washing a well and to instead wash the well with a fluid whose viscosity can be controlled and to control the formation pressures by varying the viscosity of the circulating medium.

It is a further object to provide a circulating medium which may be solidified at will to close in a well and melted when desired to permit the well to flow.

It is a further object to eliminate the necessity for setting a casing permanently in cement, and

to instead set it in a material capable of being solidified or liquefied at will so as to permit of the adjustment of the casing according to the gas-oil and oil-water levels whenever desired and the eventual removal of the casing.

Another object is to thermally insulate the casing from the wall of the hole to retard escape of heat to the surrounding formation, both from the circulating medium during drilling and from the well flow during production.

It is a further object to provide a means for positively controlling the viscosity of a circulating medium in a well.

One other object is to provide a circulating medium which will not react chemically with the formations.

Yet another object of this invention is to pro vide a means for preventing paraffin deposits on the walls of the pipe in an oil well.

Another object is to provide a means and method of protecting and preserving a core during its recovery.

Another object is to provide a method and means of surveying a well electrically as drilling proceeds.

Another object is to provide for the running of normal production tests.

Dther objects and advantages will become apparent from the following description taken in connection with the accompanying drawings, it being understood, however, that the same are by way of illustration and example only and are not to be taken as in any way limiting the scope of this invention. The spirit and scope of this invention are to be limited only by the prior art and by the terms of the appended claims.

Referring now to the drawings, in which like numerals indicate corresponding parts throughout:

Fig. 1 is a diagrammatical plan view of equipment employed at the top of a well in accordance with this invention.

Fig. 2 illustrates diagrammatically the means for heating the well casing and circulating medium in accordance with this invention.

Fig. 3 is a View partly in section, illustrating one means for connecting the resistance units on the casing to the leads from a controlling electric cable.

Fig. 4 is a view in vertical cross section illustrating the upper portion of a well being drilled in accordance with this invention.

Fig. 5 is an enlarged vertical cross section of the lower portion of the same.

Fig. 6 is a view similar to Fig. 5 illustrating an apparatus for flowing a well.

In accordance with this invention, a circulating medium such as asphalt is employed during the drilling and its viscosity regulated to positively control the natural formation pressures in the well. Means are also provided for regulating this viscosity at any point in the well. It

will be understood that this invention is not limited to the use of asphalt as a circulating medium, nor to the specific details of any of the apparatus employed. On the other hand, any substance capable of a wide range of viscosity variation and having the desirable diathermal and dielectric properties may be used, and any suitable means employed for regulating the viscosity of such substance, and for performing the other functions hereinafter described, so long as such substance and means fall within the terms of the appended claims.

Referring now more particularly to Fig. l, the numeral l indicates the derrick floor, and 2 the upright corner posts of the derrick. The customary rotary table is indicated at 3, and arranged to be driven through a suitable clutch mechanism 4.

The return pipe 5 through which the circulating medium is returned from the well after being circulated is shown emerging from below the derrick floor at the right as shown in Fig. 1, and emptying onto a shaker screen 6 through which it is passed for the purpose of removing cuttings, etc. After passing through the screen 6, the circulating medium is delivered through the discharge pipe 1 into the tank or pit 8 from which it may be pumped through a pipe 9 and pump l into the hose or the like ll leading to the drill stem.

The pipe is preferably surrounded by or provided with a heating device which in this instance is shown in the form of an electrical resistance wound upon the pipe. This electrical resistance may be supplied with electrical energy from any suitable source and under any desired control. The shaker screen 6 may be heated by means of its own resistance to the passage of a flow of electric current from any suitable source such as a battery I3 through leads l4 and 15. The heating unit l2 which surrounds the pipe 5 may be connected in series or otherwise with another heating unit I 6 surrounding the pipe 1, the purpose of all these heating devices being to maintain the circulating medium at the proper viscosity. The tank or pit 8 may likewise be provided with a heater or heating unit of suitable design if found desirable.

In like manner, the pipe 9 is provided with a heating unit I! and the pipe or hose H with a unit I8.

In operation, the well is preferably drilled with an expansible bit l9 having blades 20, and the hole is formed with a diameter such as indicated at 2|, this diameter being considerably larger than the diameter of the casing 22 which is to be employed. The lower end of this casing 22 is shown provided with a screen section 23 forming a shoe therefor and secured to the lower end of the casing at 24. This screen section or shoe is formed with substantially the same outer diameter as the internal diameter of the hole being drilled, and is of somewhat larger diameter than the casing 22.

The casing 22 is made up as illustrated in Fig. 2, a cable 25 being run into the hole along the outside of the casing and provided with connectors 26 at regular intervals, by which it may be connected to the heating units or resistances 21 wound about the respective sections of casing. The opposite end of each heating unit is grounded to the casing as indicated at 28. Preferably the heating units are wound about substantially the entire length of each section of casing with the exception of a part adjacent each end of each section of sufficient length to permit ready use of tongs or the like in screwing together the joints of the casing. The cable 25 may be unwound from a suitable drum such as 29 located beneath the derrick floor, and as each section of casing is added the heating unit which is wound thereabout is connected to the corresponding connector 26 on the cable. The cable may be bound against the outer wall of the casing if desired.

This cable is preferably formed with a large number of leads so that the respective heaters or groups of heaters may be separately supplied with electrical energy, thus permitting regulation of the temperature of the casing as desired at any particular point.

The electrical heating units may be formed and secured in place in any desired manner, but are preferably formed of steel wire enameled both before and after being wound upon the pipe.

The drill stem 30 which is driven by the rotary table 3 through the Kelly joint 3| is preferably provided with insulating and spacing rings 32 at spaced points thereon for the purpose of spacing and insulating it from the well casing 22.

The screen 23 is wound with a heating coil 33 so that it may be heated as and when desired and with an auxiliary resistance 34 for use in making a temperature survey of the formation as the drilling progresses.

In drilling a well in accordance with this invention, the circulating medium employed is of such a nature that its viscosity is capable of a wide variation according to change in temperature, but which is substantiauyaa-so1id at,ordinar atmospheric temperatures. This circulating Inseam, which in this instance may be asphalt by way of example, is kept in its fluid state during the drilling of the well by means of the various heating units which have just been described. In drilling a well according to this method, the hole is first spudded in in the customary manner, and the bit is then inserted and drilling is begun. The casing 22 with its heating units is lowered into the well as the drilling progresses, a section of casing being added each time that a section of drill pipe is added, and the lower end of the casing being preferably kept not more than two sections of drill pipe above the drill at all times. The asphalt or similar circulating medium in its fluid state, due to the temperature maintained by the various heating devices, is pumped down through the drill stem by means of the pump I0 and flows back up through the space between the drill stem and the casing. The temperature within the casing is maintained by means of the heaters surrounding the casing, and by the heat content of the asphalt introduced into the well, and as the casing is lowered into the well it will be seen that part of the asphalt will flow past the lower end of the casing and will fill the annular space between the casing and the walls of the hole. That portion along the walls of the hole, both above and below the lower end of the casing, will tend to solidify, thus forming a protection for the wall's of'the hole and preventing cave-ins and other possibly disastrous occurrences. This also forms a positive control for heaving shale formations and the like by forming an inert support and seal thereover.

During the drilling of the well the temperature of the circulating medium is so regulated by regulating the supply of energy to the various heating devices that any pressure encountered in the formation being drilled will be under control, due not to any pressure exerted against the formation but to the viscosity which is maintained in the circulating medium. Thus there is eliminated the danger of placing too great a pressure on the formation of the well and injuring or destroying future production, and at the same time ample protection is provided against blow-outs.

As the drilling of the well progresses a record may be kept of the natural temperature existing in the formation by means of from time to time shutting off the heat supplied adjacent the easing shoe and measuring the resistance of the resistance coil 34 wound about the casing shoe 23 during such times as no heat is being supplied adjacent this shoe. Only a small current is run through this coil for the purpose of measuring its resistance, and it will be seen that this resistance will vary in accordance with the natural temperature of the formation in which it is located. With this data available, it will be a comparatively easy matter to regulate the supply of energy to the respective heating units so that a substantially constant temperature of the casing may be maintained throughout the depth of the well.

With the casing temperature maintained constant, the temperature and viscosity of the circulating medium within the casing can be controlled by controlling the temperature of this medium as it enters the well. This temperature will normally be higher than the casing temperature, and by virtue of heat losses to the casing will result in a minimum temperature and a maximum viscosity at the bottom of the hole. Thus at the point where the cuttings are to be picked up the viscosity of the medium will render it most effective for this purpose.

When it is desired to test the well for production the drill may be drawn up a short distance, and by increasing the amount of heat supplied by the heating units surrounding the casing and the screen 23 the casing and screen may be lowered to any point in the formation where it is desired to make a test. Circulation may then be set up in a reverse direction so as to remove the asphalt from the drill stem, and heat is at the same time supplied to the casing screen 23 to remove the formation seal at the point where the screen is positioned and start the flow of the well up through the drill stem.

The nature of the formation being drilled may be determined at any time by measuring the resistance between the drill stem as one electrode and the casing as the other, it being noted that the asphalt being circulated is a dielectric, and that consequently these parts are insulated from each other, but that they are both in contact with the formation, one directly at the point being drilled and the other a short distance thereabove. It will be readily apparent that as soon as the drill enters a formation having a different resistance from that through which drilling has been progressing, that this can be determined by measuring the resistance between the casing and the drill stem. It is noted that the formation thus surveyed is in its natural state and has not been contaminated with electrically conductive drilling fluid.

In addition to the survey just referred to, it will be noted that since the casing and the drill stem are both insulated from the walls of the hole, except at the lower end thereof, it is possible, by means of an electrode at the surface of the ground, to locate the position of that electrode for which there will be minimum resistance between that electrode and the lower end of the casing or drill stem. The position of this point, which is thus located, will serve as an indication of the horizontal position of the lower end of the hole and thus determine the drift which has taken place, and makes possible the accurate determination of the true vertical depth of the well. Measurements can also be taken of the natural potential difference between the drill stem and said surface electrode as the drilling proceeds.

This serves as a measure ofthe spontaneous potential of the formation being drilled and of the porosity of such formation.

After the drilling isflnished and the drill stem test made, as above indicated, the drill and drill stem may then be removed from the hole and a string of tubing 35 lowered into the hole in its place. This tubing 35 may carry at its lower end a screen 36, through which the oil or other substance being produced is adapted to flow. An electric cable 31, similar to the previously described cable 25, extends down along this tubing 35 and is connected at its lower end to a head coil or unit 38 wound about the screen 26. This screen 36 is, of course, provided with openings 39 for the purpose of permitting the fluid from the well to pass through and into the tubing.

It will be understood that when the drill stem and drill are being removed from the well the lower end of the well will again be filled with asphalt, and as the lower heating units on the casing are shut off this asphalt will become substantially a solid and stop all flow from the Well. When the drill stem and drill head have been removed, and it is desired to run the tubing and screen into the well, the heater 38 on the screen is energized through the cable 31, and the screen is thus enabled to melt its way down through the asphalt in the well until the desired level is reached.

The screen 23 on the casing is also lowered to the level of the producing formation if it is not already at that point, and the heater 33 on this screen is energized. The various heating units on the casing are energized so that the entire column of asphalt within the casing becomes substantially fluid. Circulation is then set up in a reverse directionthat is, downwardly through the casing and upwardly through the tubing. Due to the fact that a relatively high temperature is being maintained, both at the surface of the formation and at the surface of the screen 36, this reverse circulation will permit the natural pressure of the oil well to force the oil through i the casing screen 23 and the tubing screen 36 and into the tubing. As soon as the flow has become well enough established the heat to the respective screens may be shut off, and the well will continue to flow in the ordinary manner. In the meantime, the asphalt in the casing surrounding the tubing Will solidify to a greater or less extent and will serve to support the tubing.

It is noteworthy that if it be found that the fluid being produced from the well has too great a quantity of gas therein, indicating that the upper end of the casing screen, as well as the upper end of the tubing screen, is partially above the gas-oil horizon, the casing may be lowered by simply energizing the heating units mounted thereon until the lower end of the casing is sulficiently below this horizon, so that the ratio of gas and oil is cut down by any desired amount. On the other hand, if it be found that the well is producing partly salt water, thus indicating that the tubing screen is partially below the oilwater horizon, the tubing may be raised by energizing the heating units on the casing, as well as those on the tubing screen, and then by permitting the asphalt below the tubing screen to solidify and form a support for the tubing screen. The adjustments indicated for both the casing and the tubing may be made not only at the time production is started but at any time during the life of the well, so as to provide for the changes in the producing conditions.

It would seem from the foregoing that by the method and apparatus set forth there is formed on the walls of the drilled hole as the drilling proceeds a protective and sealing coating which serves not only to support the walls of the hole but to seal the same against the ingress into the hole of any undesired material contained in the formation which has been drilled. It is further apparent that there has been provided a means whereby the casing may be supported within the hole at any position desired and may be adjusted in there to meet whatever conditions may be encountered. In addition to the foregoing, there has been set forth a method of drilling a well and of producing the same whereby the greatest dangers ordinarily involved in these operations are eliminated and the well is positively controlled without danger of injuring it.

It is further apparent that the coating which is formed on the walls of the hole and the body of asphalt which remains within the casing after the tubing has been run and production started serves as an insulator to prevent heat from escaping to the surrounding formation from the fluid which is being produced by the well. This naturally conserves the heat which is naturally present in this fluid and thus prevents it from losing the natural energy which it possesses. The energy of the well is thus conserved and its natural .flow period greatly prolonged.

In addition to the foregoing, it will be seen that when the natural energy of the formation at the bottom of the hole becomes depleted it will be possible to supplement the same by supplying heat energy thereto from the heating units which are wound about the casing.

A method and apparatus have been set forth which are capable of carrying out all the objects and advantages sought by this invention. It is to be noted, however, that the disclosure is purely by way of illustration and that the method set up is not limited to the drilling and production of oil alone, but may be utilized for the production of various other substances obtainable from wells. It is further noted that the invention is not limited to the use of asphalt as a circulating medium because of the fact that there are various other media, having equally desirable characteristics, which may be employed. It is also noted that the apparatus shown and described may be varied as desired, so long as it remains capable of carrying out the method claimed in the appended claims.

Having described my invention, I claim:

if 1. The method of taking a core from a well m r --I hole comprising cutting said core with a core drill, during said cutting operation circulating a heated substance adapted to substantially solidify when cooled, and permitting a portion of said substance to cool on the core as it is being cut to form a protective and retaining sheath thereon.

2. The method of drilling a well which comprises circulating through the hole while drilling the same a liquid substance substantially solid at atmospheric temperatures, lowering a casing into the hole as the depth of the hole is increased, normally supplying heat to said substance suflicient to maintain in its liquid state the circulating substance within the casing and to permit that without thg gasingto sglidjix and supplying additional heat suflicient to partly liquefy that portion of the circulating substance without the casing when it is desired to lower or raise the casing.

3. In a method of well drilling, the steps of circulating through the well during drilling a substance of widely variable viscosity, supplying heat to said substance to render it sufiiciently liquid to circulate, but sufiiciently viscous to control formation pressures, casing the major portion of the walls of the well and screening a portion thereof opposite a producing formation, heating the screenedcportion of the well, and circulating said substance down through an annular portion of the well and in through said screened portion to induce production of the formation opposite the screened portion of the well to flow through said screened portion and up through the centra1 part of the well.

4. The method of drilling a well which comprises circulating through the well while drilling the same a substance of widely variable viscosity dependent upon its temperature, determining the natural terngg aturgs of the various forri'atio'ns through which the well is drilled as the, depth of the hole increases, and supplyin heat at various points of the depth of said hole in such quantities respectively as will maintain a substantially uniform temperature throughout the depth of the hole. 5. The method of taking a core from a well ,I-IOWARD L. REED. 

